1. Field of the Invention
The present invention relates to a photosensitive lithographic printing plate processing apparatus which is capable of replenishing processing solutions such as a gum solution for protecting a surface of a photosensitive lithographic printing plate, which has been processed for development, or a plate baking conditioner which is applied to the surface prior to baking treatment.
2. Description of the Related Art
A photosensitive lithographic printing plate, which has images printed thereon by a printing apparatus, is sent into a photosensitive lithographic printing plate processing apparatus in which the photosensitive lithographic printing plate is advanced in order through: a developing tank, where the photosensitive lithographic printing plate is subject to developing processing; a rinsing or washing tank, where the photosensitive lithographic printing plate is washed; and a desensitizing or finisher tank, where a gum solution (or a finisher solution) is applied to the photosensitive lithographic printing plate. Such application of the gum solution protects a surface of the photosensitive lithographic printing plate which has passed through developing and washing processes. The photosensitive lithographic printing plate is ejected from the photosensitive lithographic printing plate processor after a final stage, i.e., a drying process, is completed.
While being conveyed through the above developing tank, the photosensitive lithographic printing plate is immersed in a developing solution within the tank, or the developing solution is sprayed onto the surface of the photosensitive lithographic printing plate. The photosensitive lithographic printing plate is thereby subject to developing processing. Since the developing solution becomes progressively fatigued as the developing processing proceeds, the developing solution is replenished from a replenishing device in accordance with a degree of fatigue of the developing solution. The fatigue of the developing solution is defined as the activity of the same, and is estimated from measurements of the electric conductivity or pH of the developing solution or from developing-processing time and amount. On the basis of the results therefrom, the developing solution is replenished so that the activity thereof increases.
In addition, the surface of the photosensitive lithographic printing plate, which has been subject to developing processing, is protected by the gum solution (or the finisher solution) being applied thereto. However, since the gum solution is evaporated by heat that results from ambient temperatures or the drying process, changes in the concentration of the gum solution occur easily. In particular, since such a gum or finisher process is followed by the drying process, the gum or finisher solution is subject to heat, which results in evaporation. To overcome this drawback, a method has been used in which an evaporation amount of the gum solution is estimated (from experimental results, for example) in accordance with the environment in which the photosensitive lithographic printing plate is used (i.e., ambient temperature or humidity, drying air, and the like). The gum solution is replenished with a corresponding amount of water at definite time intervals or in accordance with the amount of the plate to be processed, thereby permitting concentration of the gum solution to be maintained within predetermined ranges. In order to accomplish the original function of the gum solution, a predetermined amount of gum solution of a predetermined concentration must be applied to the plate. However, the properties of the concentration of the gum solution and those of the activity of the developing solution are different. For example, the conductivity or pH of the gum or finisher solution greatly varies because components of the developing solution, which is located upstream of the gum or finisher solution, may become mixed in with the gum or finisher solution. However, such variations do not affect the function of the gum or finisher solution. The gum solution is replaced when a certain time or amount of processing is made to the photosensitive lithographic printing plate or when the gum solution becomes extensively contaminated.
In this way, the photosensitive lithographic printing plate processor is arranged to maintain a constant concentration of the gum solution in order to apply a certain amount of the gum solution to the surface of the photosensitive lithographic printing plate, thereby protecting the plate.
Further, in order to improve the printing durability of the printing plate, the surface of the printing plate is sometimes supplied with a plate baking conditioner before application of the gum solution thereto so that the surface is affinitizing. Thereafter, baking processing is effected. However, the affinitizing solution is also subject to evaporation under the influence of heat which radiates from a baking station at the subsequent process. In addition, the concentration of the gum solution or the affinitizing solution is sometimes regulated so as to be decreased for some reason.
A drawback of the above is that it is troublesome to set an amount of replenishment water for each change in application environments of the photosensitive lithographic printing plate processor. In particular, if the amount of replenishment water, which is based on processing time, does not match any application environment of the photosensitive lithographic printing plate processor, the concentration of the gum solution or the affinitizing solution consequently falls outside of a predetermined range. This makes it impossible to apply a certain amount of the gum solution or the affinitizing solution to the surface of the photosensitive lithographic printing plate. In addition, the thickness of a protective layer of the gum solution or the affinitizing solution adhering to the surface of the photosensitive lithographic printing plate is reduced. As a result, the plate surface cannot be provided with protection of uniform quality. As can be seen from the above, the replenishment amount is difficult to regulate precisely in accordance with various application environments or inherent misoperations of the photosensitive lithographic printing plate processor. This results in complicating the operation of the photosensitive lithographic printing plate processor.